3 A/P Biology
Plant Organelles
Pages 112-121
The plant cell has almost all the cellular inclusions that the animal cell has. In
fact, the plant cell has some unique characteristics that define it as a plant cell. The plant
cell differs from the animal cell by containing three structures NOT found in the animal
cell- they are:
1.) The plant cell has a cell wall (in addition to a cell membrane or plasma
membrane).
2.) The plant cell contains chloroplasts (these chloroplasts can contain special
pigments that can convert light energy into chemical or food energy)
Chloroplasts, like mitochondria, have their own DNA (circular DNA) and can
replicate independently of the plant cell!
3.) The plant cell has a large water vacuole (containing mostly water).
Below you will see a picture of a typical plant cell:
If you compare the plant cell diagram to the animal cell diagram, you will note
many similarities. Many of the cell inclusions are the same (they look the same and have
the same function in each type of cell). One unusual difference between the plant cell and
an animal cell is the disposition of centrioles. Animals cells have them, plants do not.
They BOTH have a “centrosome” or microtubule organizing center. This is a generalized
“area” where microtubules are produced to move chromosomes during mitosis and
meiosis.
Page 2 (Cont. A/P Biology Packet #3
I mentioned chloroplasts earlier, however different plants have other “plastids”
that contain other pigments such as xanthenes and carotenes (that are typically found in
chromoplasts) and some vacuoles contain starch material (amyloplasts) that are clear. I
would like to first show a somewhat simplistic representation of how a mitochondria and
then chloroplasts MAY have been incorporated into one of the earliest cells. (See below.)
It is important to note that animal cells incorporated the mitochondria in the
representation (as well as fungi and non-plant-like cells) and the plant cell evolved by
taking in the mitochondria AND the chloroplasts (endosymbiosis, mutualism).
Let us look at the three different organelles that make the plant cell different from
the animal cell. I will start with arguably the most important difference.
Chloroplasts The chloroplasts are actually very complex structures that usually contain
Chlorophyll “A” and “B” that can absorb light. Below we see a picture of a typical
chloroplast. It is important to note that BOTH mitochondria and chloroplasts contain
their OWN DNA and can therefore replicate inside cells ON THEIR OWN!
So- when
energy requirements
inside either the
animal cell OR the
plant cell change,
mitochondria and
chloroplasts can
increase their
numbers by simply
dividing. The more
chloroplasts
available, the better
Page 3 (Cont. A/P Biology Packet #3)
the plant cell can make chemical energy from sunlight (through photosynthesis). By the
same token, the more energy the plant OR animal cell needs in the form of Adenosine
Triphosphate – abbreviated ATP- the energy “currency” of the animal or plant cell, the
more mitochondria will be created (through simple division or fission). Mitochondria
allow both animal AND plant cells to breakdown glucose efficiently. Chloroplasts allow
plant cells to convert light energy into chemical energy (glucose).
One important thing to think about is that not all plants/leaves are green. Some
are red, some are yellow, and some are even brown in color. There are many different
pigments found in plants that can absorb sunlight energy. The chloroplast is a specialized
member of a family of related plant organelles called plastids. Amyloplasts can be
colorless plastids that store starch (long chains of sugar molecules stuck together).
Chromoplasts have pigments that give fruits and flowers their orange and yellow hues.
Plastids that have green pigments called chlorophyll are the chloroplasts. The
chloroplasts contain the green chlorophyll pigment and enzymes that help photosynthesis
take place. (From: Campbell, N.A. and Reece, J. B. 2002. Biology. Benjamin Cummings.
New York. p. 124)
There are many different pigments that can help convert sunlight energy into
chemical energy (food). Perhaps the most common are chlorophyll a and chlorophyll b.
These pigments are found in ALL green plants and the pigments are expectedly, green.
The chloroplast has two important functions: (1) absorb light (through a light
dependent reaction)- this absorption of light taking place in the thylakoids (see
diagram). (2) contains the Calvin Cycle (a series of enzymes complexes) that
incorporates carbon dioxide molecules into sugar molecules- this part occurs in the
stroma (see diagram- pg. 2 bottom rt.).
Cell Wall Plant cell walls function primarily as rigid structures to give plant cells shape
and resist turgor pressure. The cell wall is formed by repeating units (each unit is
referred to as a monomer) of
glucose called cellulose.
(Absorbent cotton is one of the
purest forms of cellulose.) The
cellulose polymers (cellulose
polymers are many glucose
molecules stuck together) form
microfibrils that are laid down
randomly. (See picture to
right.) Interspersed in the
secondary cell wall matrix is a
compound called lignin. This
is what helps make fruits and
vegetables crunchy and
contributes to fiber in our diet.
"Lignin is actually not one
compound but many. All are
Page 4 (Cont. Handout #3 AP Bio)
complex, amorphous, three-dimensional polymers that have in common a phenyl propane
structure, that is, a benzene ring with a tail of three carbons. In their natural unprocessed
form, they are so complex that none of them has ever been completely described, and
they have molecular weights that my reach 15,000 or more." (Taken from: McCrady, E.
(1991). The Nature of Lignin. Avail: http://cool.conservationus.org/byorg/abbey/ap/ap04/ap04-4/ap04-402.html, pg. 1) Another view of 1o cell wall.
Individual fibers look like this:
You can imagine
how many
trillions of sugar
molecules it takes
to make a cell
wall for a plant.
To show the complexity and construction of these cell walls, go to:
www.ceres.net
then go to pull down menu: About us
Biofuels
Carbohydrates and cell walls
Then “Click on the tabs marked: Cellulose, lignin, etc…
Page 5 (Cont. #3 Handout A/P Biology)
This primary cell wall is
relatively thin and flexible.
When the plant cell has stopped
growing, a tougher, stronger cell
wall is laid down just below the
primary cell layer. This is
called the secondary cell wall.
(Located between the cell
membrane and the primary cell
wall.) The function of the cell
wall is to allow the plant cell to
resist water pressure (it is
thought that the presence of
lignin is responsible for this
turgor pressure resistance) that
can build up within the plant
cell. The plant cell does not
maintain an osmotic balance
like the animal cell. Water
moving into the plant cell
(influx of water) can be
tolerated because the cell walls Middle lamella
are rigid and help prevent the
made of Pectin-glue
cell from bursting. It MUST be that holds plant cells
noted that water is necessary for together
photosynthesis to take placetherefore, the ability to store
water is essential to the life of the plant! An internal hydrostatic pressure (hydrostatic
pressure=water pressure) builds up within the cell, eventually equalizing the osmotic
pressure and preventing further influx of water (this is called turgor pressure). The
turgor pressure gives the plant cell shape, strength, and rigidity. Moreover, this turgor
pressure prevents plants from wilting and gives specialized plant cells (xylem and
phloem) strength enough to move water great
distances from the roots to the leaves.
Large water vacuole: The large water vacuole is
primarily used to store water, food (especially
sugar products), waste products, and salts. The
water vacuole also helps give the plant cell shape
and rigidity. Turgor pressure can cause the cell
vacuole to elongate by taking in water, which is
accumulated in the large central vacuole and
makes the cell longer (and larger). See picture to
the right. When the cell stops growing, the
secondary cell walls are laid down and the cell
Page 6 (Cont. Handout #3 AP Biology)
becomes more rigid and stable.
The movement of water through a plant depends on a balance between the water
inside the plant cell and outside the plant cell. The movement of water throughout the
plant (via xylem) is controlled by physical properties of water being attracted to each
other (cohesion) and water attraction (interacting) with other surfaces (adhesion).
Additional forces that help move water in the plant are osmotic pressure- the movement
of water from an area of higher concentration to an area of lower concentration. The
production of sugar is involved in this osmotic process!
Answer 15 questions Here and on your scan tron- short answer on these sheets only!
_____ 1.) Plant cells contain the following different organelles compared to the animal
cells EXCEPT for this organelle (found in both cells):
a.) chloroplasts b.) mitochondria c.) large water vacuole d.) cell wall e.) none of these
_____ 2.) Plant cell contain all of the following structures EXCEPT:
a.) cell wall b.) cell membrane c.) mitochondria d.) chloroplast e.) none of these
_____ 3.) Mitochondria are beneficial to both animal cells and plant cells because they:
a.) allow the cells to convert light energy to chemical energy
b.) allow cells to efficiently breakdown sugar to form ATP
c.) allow the cells to maintain turgor pressure
d.) allow cells to perform osmosis
e.) none of the above are correct
_____ 4.) Chloroplasts:
a.) are specialized plastids
b.) contain light absorbing pigments
c.) help the plant cell convert light energy to chemical energy
d.) can divide on their own depending on demand for chemical energy
e.) all of the above are correct
_____ 5.) All light absorbing plant pigments are (Internet):
a.) green
b.) green or yellow
c.) green, yellow, or red
d.) green, yellow, red, or brown
e.) plant pigments can be many different colors
_____ 6.) Amyloplasts are structures that:
a.) store amino acids to help build protein
b.) store starch for energy reserves
c.) store water, waste, and salts to create turgor pressure
d.) store ATP for plant cell function
e.) none of the above are correct
Page 7 (Cont. #3Handout A/P Biology)
_____ 7.) Chromoplasts are structures that:
a.) store amino acids to help build protein
b.) store different plant pigments
c.) store waste, water, and salts to create turgor pressure
d.) store ATP for plant cell function
e.) store starch for energy reserves
_____ 8.) Plastids that contain green pigments are called:
a.) mitochondria b.) amyloplasts c.) myloblasts d.) centrioles e.) none of these
_____ 9.) The location of the absorption of light in most plants is called:
a.) amyloplasts b.) chlorakoids c.) neuroplast d.) angioplasty e.) thylakoids
_____ 10.) Secondary cell walls are made up of:
a.) protein and bi-lipid material
b.) protein only
c.) bi-lipid material only
d.) repeating units of amino acids
e.) repeating units of sugars and lignin
_____ 11.) The primary cell wall is:
a.) made of a very rigid cellulose structure
b.) made up of a flexible cellulose structure
c.) made up of proteins and bi-lipid membranes
d.) made up of protein receptors
e.) none of the above
_____ 12.) The secondary cell wall is:
a.) made up of repeating glucose units
b.) more rigid than the primary cell wall (helps resist turgor pressure)
c.) laid down between the cell membrane and the primary cell wall
d.) produced only when the plant cell has stopped growing
e.) all of the above are correct
_____ 13.) What is the function of turgor pressure?
a.) causes the cell wall to lose its rigidity
b.) creates a negative osmotic gradient
c.) slows down photosynthesis
d.) moves water from an area of lower concentration to an area of higher
concentration
e.) gives plant cell shape, rigidity, and strength
Page 8 (Cont #3 Handout A/P Biology)
_____ 14.) What factor directly causes the plant cell to get larger?
a.) increased photosynthesis
b.) more mitochondria
c.) water vacuoles losing water
d.) plant cell nucleus transferring water to large water vacuole
e.) increased turgor pressure within the large water vacuole
_____ 15.) What causes a plant to wilt?
a.) increased turgor pressure in the large water vacuole
b.) addition of a secondary cell wall
c.) subtraction of a primary cell wall
d.) decreased photosynthesis
e.) decreased turgor pressure
Answer the following questions on this handout only!
16.) Explain why it was advantageous for Ancient Prokaryotes to incorporate
mitochondria into their cells. Also, explain why some ancient prokaryotes incorporated
chloroplasts as well as mitochondria. Speculate the effect of an ancient prokaryote only
incorporating chloroplasts and NOT mitochondria into the cell.
17.) Where would chlorophyll a and chlorophyll b most likely to be found? If a plastid
was green, what type of plastid would it be? If the plastid contained red and yellow
pigments, what would it be called? In the Fall- green leaves turn to different colors.
Based on the information you have already (and any you can garner from the Internet),
why do leaves turn other colors? Also, during the time they are not green, do they still
perform photosynthesis?
18.) If you are given the information that plant and plant-like organisms are the MAJOR
sources of oxygen (due to the function of chloroplasts performing photosynthesis),
speculate what might have happened if chloroplasts were never incorporated into
prokaryotic cells (I am looking for global effects such as air quality, temperature, animal
life, plant life, etc.. Hint: this loss of chloroplasts moving into prokaryotic cells would
prevent the evolution of plants as we know it…)
Date: ____________________
Lesson Plan for Handout #3 AP Biology
Objective: TLWD ability to name all the cell components found in plant cells, determine
which inclusions are found in plant cells and not in animals cells and determine the
function of all plant cell inclusions, know what they look like and explain why plant cells
are different from animal cells when given handout #3.
Content: Plant cell organelles and function, variation of cell inclusion from animal cells
Method: Handout #3
Homework: Complete #3
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